Selective Anion Anchoring in MOF-Based Supercapacitors Revealed with Operando Small-Angle X-Ray Scattering

Malina Seyffertitz, Chloe J. Balhatchet, Max V. Rauscher, Sebastian Stock, Gerhard Fritz-Popovski, Thomas Leiner, David Holec, Heinz Amenitsch, Alexander C. Forse and Oskar Paris ()
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Malina Seyffertitz: Montanuniversität Leoben
Chloe J. Balhatchet: University of Cambridge
Max V. Rauscher: Montanuniversität Leoben
Sebastian Stock: Montanuniversität Leoben
Gerhard Fritz-Popovski: Montanuniversität Leoben
Thomas Leiner: Montanuniversität Leoben
David Holec: Montanuniversität Leoben
Heinz Amenitsch: Graz University of Technology
Alexander C. Forse: University of Cambridge
Oskar Paris: Montanuniversität Leoben

Nature Communications, 2025, vol. 16, issue 1, 1-11

Abstract: Abstract Understanding how ions interact with electrodes in electric double-layer capacitors (EDLCs) is key to advancing energy storage, yet many fundamental aspects remain unclear. Here, we employ operando small-angle X-ray scattering (SAXS) to investigate charge storage in metal-organic framework (MOF)-based supercapacitor electrodes as a model system. Using Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) MOF electrodes and 1 M aqueous sodium bis(trifluoromethanesulfonyl)imide (NaTFSI) as the electrolyte, we show that TFSI- anions are immobilised near MOF pore walls via fluorine-hydrogen interactions with N-H functional groups of the MOF. We quantify the concentration of pinned anions and demonstrate that their immobilization persists across different applied cell voltages, resulting in a cation-dominated charge storage mechanism governed solely by Na+ adsorption and desorption. Charge balancing is unaffected by whether voltage is applied stepwise or gradually, with no dynamic differences between in-pore and out-of-pore environments and no ion intercalation taking place.

Date: 2025
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DOI: 10.1038/s41467-025-63772-w

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